This invention is concerned with determining the condition of a fluid. A wide variety of fluids, such as lubricants, coolants, fuels, hydraulic fluids, paints and coatings, are used in many different types of machines and processes, such as aircraft, ground vehicles, ships, pumps, and manufacturing. The properties of such fluids can have a significant effect on the performance of the machine or process in which the fluid is utilized. Degradation of a fluid property can cause the system to operate at less than optimum efficiency or can even cause catastrophic failure and unscheduled downtime. Degradation of the mechanical and chemical properties of a lubricating fluid, for example, and the cleanliness of the lubricant, are all well known factors in degrading the performance of the machine being lubricated.
Consequently, the ability to accurately characterize such fluid properties can increase the efficiency of the machine or process involved. The increased efficiency can result not only in helping to extend the useful life of the machine and avoiding catastrophic failures from using degraded lubricants, but also in reducing cost through employing a lubricant for substantially all of its useful life, rather than discarding it prematurely. A common maintenance approach, for example, is to estimate the useful life of the lubricant and establish a fixed replacement interval for the lubricant based on the estimate. This practice, however, typically results in replacement of lubricants that have substantial remaining useful life. By contrast, the approach can also occasionally result in considerable damage to a machine or system when a lubricant experiences an unusually short lifetime and degrades before the fixed replacement interval has been reached.
For these reasons, it is desirable to be able to determine the current health and condition of a fluid and to also have the capability to predict the remaining useful life of a fluid.
A variety of techniques are known in the art for monitoring the properties of fluids. Some of these techniques, however, require observations to be made over a relatively long period of time in order to establish a trend in the fluid properties. Other techniques are too qualitative to produce data that can accurately characterize the fluid properties. In addition, some of these approaches, such as extracting a sample from the fluid and transporting the sample to a remote location for chemical analysis, are excessively time consuming and expensive.
Therefore, a need has developed in the art for a fluid diagnostic technique which can be performed locally on a small sample of the fluid, and which imposes minimal or no interference with the operation of the associated machine or process. Moreover, it would be advantageous to provide such a technique capable of fully evaluating the fluid to the point of failure.